Thermo-volumetric motor

ABSTRACT

A thermo-volumetric motor (10) includes a continuous incompressible fluid path in the form of a hydraulic oil path (12), a continuous compressible fluid path in the form of a refrigerant path (14), and a solar collector (18). The solar collector (18) is adapted to absorb heat from a heat source, in this example, sunlight. The hydraulic oil path (12) includes a pressure transfer mechanism, in this example a pair of hydraulic cylinders (20A, 20B) located in a parallel flow arrangement. The oil path (12) further comprises an actuating device, in this example a hydraulic loader (22), in fluid communication with a first heat exchanger (24). The refrigerant path (14) comprises a pump (28) operatively coupled to the hydraulic motor (22), and a heat transfer device, in this example a second heat exchanger (25). The refrigerant path (14) further comprises a cooling unit, in this example a first accumulator or condenser (32), used for cooling the refrigerant. The second heat exchanger (25) comprises a shell and tube arrangement wherein refrigerant is passed through a helical tube, and a first phase change substance, such as sodium acetate trihydrate, is contained within the shell.

FIELD OF THE INVENTION

The present invention relates generally to a thermo-volumetric motor andrelates particularly, though not exclusively, to a hydraulically driventhermo-volumetric motor. More particularly, the present inventionrelates to a hydraulically driven thermo-volumetric motor whichexchanges heat with a phase change substance having a relatively highlatent heat of fusion. The present invention further relates to a methodfor generating motion by using energy stored in the form of latent heat.

BACKGROUND OF THE INVENTION

There are a myriad of motors which are commercially available. Themotors are usually driven by combustible fuels, electricity, solarenergy, or a combination of any one or more of these sources of energy.Each energy source has its own drawbacks. For example, most combustiblefuels when burnt produce gases which are harmful to the environment.Furthermore, if the fuel is not completely burnt the unburnt fuel can beexhausted and also adversely affect the environment.

Alternative sources of energy, such as photovoltaic generatedelectricity has been used for driving motors. Electricity in remoteareas is somewhat restricted in that the storage of sufficientquantities of electrical energy in, for example, batteries takes uplarge amounts of space, is relatively expensive, and can also beextremely heavy. Solar energy is inherently restricted for at least thefollowing reasons. Solar energy is only available during sunlight hoursand may vary in intensity depending on the season of the year.Particularly cold areas of the world may never lend themselves to solarenergy as an alternative energy supply. Furthermore, photovoltaicgenerated electricity is relatively expensive to produce.

When solar energy has been used as an energy source it is usuallyabsorbed on a collector panel. The absorbed heat from the panel is thenexchanged with a fluid, in the form of specific heat, and ultimatelyused in a variety of ways to drive a motor or generator. Relativelysmall quantities of energy can be stored in the form of specific heatand solar powered electric motors, for example, have relatively littlepower. Furthermore, solar energy when used to drive a motor or generatoris limited by the cost of photovoltaic cells and storage batteries.

SUMMARY OF THE INVENTION

An intention of the present invention is to provide a thermo-volumetricmotor which can operate relatively efficiently and environmentallysafely.

According to a first aspect of the present invention there is provided athermo-volumetric motor comprising:

a continuous incompressible fluid path, adapted to carry a substantiallyincompressible fluid, said incompressible fluid path having pressuretransfer means and actuating means in fluid communication with eachother;

a continuous compressible fluid path being adapted to carry asubstantially compressible fluid, said compressible fluid path includingheat transfer means in fluid communication with the pressure transfermeans, the heat transfer means including a first phase change substancehaving a relatively high latent heat of fusion, and cooling means influid communication with the heat transfer means and the pressuretransfer means whereby, in use, heat from a heat source can be absorbedby the first phase change substance so that at least a portion of thefirst phase fuses and thereafter when said portion of the first phasechange substance solidifies and releases latent heat the compressiblefluid can absorb said latent heat and expand, thus moving the pressuretransfer means wherein the incompressible fluid is forced along theincompressible fluid path thus moving the actuating means which can beadapted to provide motive power, the cooling means thereafter coolingthe compressible fluid after said compressible fluid is released fromthe pressure transfer means.

Preferably, the compressible continuous fluid path further comprises apump operatively coupled to the actuating means and in fluidcommunication with the heat transfer means, the cooling means, and thepressure transfer means wherein movement of the actuating means drivesthe pump thereby pumping the compressible fluid through the compressiblefluid path.

Typically, the thermo-volumetric motor further comprises a collector inheat conductive communication with the heat transfer means whereby, inuse, heat absorbed by the collector from a heat source can betransferred to the first phase change substance included in the heattransfer means.

Preferably, the pressure transfer means comprises a piston slidablyreceived in a cylinder defining a compressible fluid chamber on one sideof the piston, said compressible fluid chamber adapted to receive thecompressible fluid, and an incompressible fluid chamber on an oppositeside of the piston, said incompressible fluid chamber adapted to receiveincompressible fluid whereby, in use, expansion of the compressiblefluid as effected by the heat transfer means can move the pistonrelative to the cylinder thereby forcing the incompressible fluidthrough the incompressible fluid path.

Preferably, the pressure transfer means comprises a first and a secondpiston each slidably received in a first and a second cylinder,respectively, defining a compressible fluid chamber on one side of thepiston, said compressible fluid chamber adapted to receive thecompressible fluid, and an incompressible fluid chamber on an oppositeside of the piston, said incompressible fluid chamber adapted to receivethe incompressible fluid whereby, in use, compressible fluid can beexpanded into the compressible fluid chamber of the first cylinderwherein the first piston is moved relative to the first cylinder therebyforcing the incompressible fluid through the incompressible fluid pathand moving the second piston relative to the second cylinder, andthereafter compressible fluid can be expanded into the compressiblefluid chamber of the second cylinder.

Typically, the cooling means is a first accumulator containing a secondphase change substance having a relatively high latent heat of fusionand a relatively low melting-point whereby, in use, heat from thecompressible fluid can be absorbed by the second phase change substancethus cooling the compressible fluid passing through the cooling means.

In one embodiment, the thermo-volumetric motor further comprises a heatexchanger in fluid communication with both the actuating means and thecooling means whereby, in use, heat generated by the incompressiblefluid when forced from the pressure transfer means can be transferred tothe compressible fluid via the heat exchanger thus expanding thecompressible fluid.

Alternatively, the heat transfer means further includes the heatexchanger so that heat generated by the incompressible fluid when forcedfrom the pressure transfer means can be transferred to the compressiblefluid via the first phase change substance included in the heat transfermeans.

Typically, the collector is a solar collector adapted to absorb sunlightbeing the heat source. Alternatively the heat source may be a waste heatsource.

In one example, the actuating means is a hydraulic motor.

Typically, the heat transfer means comprises:

a first tube adapted for carrying the compressible fluid through theheat transfer means; and

a shell containing the first phase change substance said substance inheat conductive communication with the first tube whereby, in use,latent heat can be transferred from the first phase change substance tothe compressible fluid via the first tube of the heat transfer means.

More typically, the heat transfer means further comprises a jacketsurrounding the shell and adapted to carry a heat transfer fluidwhereby, in use, heat from the heat transfer fluid can be transferred tothe first phase change substance thereby melting the first phase changesubstance and storing latent heat.

In this embodiment, the jacket is in heat conductive communication withthe collector wherein heat absorbed by the collector can be transferredto the first phase change substance via the heat transfer fluid.

In another embodiment the heat transfer means further comprises a secondaccumulator containing a third phase change substance, said secondaccumulator in heat conductive communication with the collector, whereinthe heat transfer fluid can be preheated by the latent heat of the thirdphase change substance before said heat transfer fluid flows to thejacket.

According to a second aspect of the present invention there is provideda method for producing motive power comprising the steps of:

absorbing heat, from a heat source, on a first phase change substanceincluded in heat transfer means wherein at least a portion of the firstphase change substance fuses, said first phase change substance having arelatively high latent heat of fusion;

transferring latent heat from the first phase change substance, uponsolidification thereof, to a compressible fluid thereby expanding thecompressible fluid;

releasing the expanded compressible fluid into pressure transfer meansthus moving the pressure transfer means which then forces anincompressible fluid through an actuating means thus producing motivepower from the actuating means; and

cooling the compressible fluid and returning said compressible fluid inthe heat transfer means.

Preferably, the method further comprises the step of driving a pumpoperatively coupled to the actuating means wherein the compressiblefluid is pumped to the heat transfer means using the pump.

More typically, the method further comprises the step of absorbing heatfrom the heat source onto a collector, wherein the absorbed heat can betransferred to the first phase change substance of the heat transfermeans.

Preferably, the step of cooling the compressible fluid involvesabsorbing heat from the compressible fluid by exchanging heat with asecond phase change substance, having a relatively high latent heat offusion and a relatively low melting-point, wherein the compressiblefluid is cooled.

Typically, the method further comprises the step of transferringspecific heat from the incompressible fluid, said specific heatgenerated when the incompressible fluid is forced from the pressuretransfer means, to the compressible fluid via a heat exchanger.

Typically the first, second and/or third phase change substances arefirst, second and/or third hydrate salts, respectively, each having arelatively high latent heat of fusion.

More typically, the first hydrate salt and the third hydrate salt has amelting-point of between 0° C. to 100° C.

Preferably, the first hydrate salt and the third hydrate salt each has alatent heat of fusion of greater than 50 kilocalories/liter (kcal/l).

In one example, the first hydrate salt and/or the third hydrate saltcomprises sodium acetate trihydrate or a derivative thereof.

Typically, the second hydrate salt has a melting-point of less than 0°C.

In one example, the second hydrate salt comprises a stoichiometricmixture of sodium chloride, calcium chloride, and demineralised water.

Typically, the incompressible fluid is a liquid hydrocarbon, such as oilor a derivative thereof.

Preferably, the compressible fluid is a refrigerant such as methane,chloro-difluoro or a derivative thereof.

More preferably, the refrigerant does not contain a halogen element.

BRIEF DESCRIPTION OF THE DRAWING

In order to achieve a better understanding of the nature of the presentinvention preferred embodiments of an apparatus and method relating to athermo-volumetric motor will now be described in some detail, by way ofexample only, with reference to the accompanying drawing in which:

FIG. 1 is a schematic of a preferred embodiment of a thermo-volumetricmotor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIG. 1, a thermo-volumetric motor 10 comprises: a continuousincompressible fluid path in the form of a hydraulic oil path 12, acontinuous compressible fluid path in the form of a refrigerant path 14,and a solar collector 18. The hydraulic oil path 12 and refrigerant path14 are adapted to carry a hydraulic oil and a refrigerant fluid, in thisexample methane chloro-difluoro or a derivative thereof, respectively.The solar collector 18 is adapted to absorb heat from a heat source, inthis example sunlight.

The hydraulic oil path 12 includes pressure transfer means in thisexample a pair of hydraulic cylinders 20A, 20B located in a parallelflow arrangement. The oil path 12 further comprises actuating means, inthis example a hydraulic motor 22, in fluid communication with a firstheat exchanger 24. Downstream of the first heat exchanger 24, the oilpath 12 further comprises an oil reservoir 26, located upstream of thehydraulic cylinders 20A, 20B. In this example, the oil reservoir has acapacity of approximately twenty (20) liters of hydraulic oil. The firstheat exchanger 24 comprises a shell through which the oil flows, and atube through which the refrigerant flows and absorbs heat from the oil.

The refrigerant path 14 comprises a pump 28 operatively coupled to thehydraulic motor 22, and heat transfer means, in this example a secondheat exchanger 25. The refrigerant path further comprises an injector orfirst pair of solenoid actuated valves 30A,30B located upstream of thehydraulic cylinders 20A, 20B respectively and cooling means locateddownstream of the hydraulic cylinders 20A, 20B, in this example a firstaccumulator or condenser 32 used for cooling the refrigerant. The secondheat exchanger 25 is located downstream of the condenser 32, the pump28, and the first heat exchanger 24. The pump 28 is rotationally drivenby the hydraulic motor 22 via an endless belt 34. Alternatively the pump28 may be driven by the hydraulic motor 22 via a gear train. Each of thefirst solenoid actuated valves 30 has a downstream flow path connectedto one of the hydraulic cylinders 20.

In this embodiment each of the hydraulic cylinders 20A, 20B comprises apiston 36A, 36B slidably received in a cylinder 38A, 38B, respectively.On one side of each of the pistons 36A, 36B there is a compressiblefluid chamber 40A, 40B and on an opposite side of each of the pistons36A, 36B there is an incompressible fluid chamber 42A, 42B. Thecompressible fluid and incompressible fluid chambers 40, 42 are eachadapted to carry the refrigerant and the hydraulic oil, respectively.

The second heat exchanger 25 comprises a shell and tube arrangement (notshown) wherein the refrigerant is passed through a first tube formed inthe shape of a triple-helix. The shell contains a first phase changesubstance, in this example a first hydrate salt comprising sodiumacetate trihydrate, having a high latent heat of fusion and amelting-point of approximately 58° C. The second heat exchanger 25 ishoused in a sealed jacket 53 surrounding the shell and adapted to carrya heat transfer fluid, in this example water. The jacket 53 has an inlet45 for receiving water and an outlet 47 for discharging water.

The heat transfer means further includes a second accumulator 16containing a third phase change substance having a relatively highlatent heat of fusion. The third phase change substance is contained ina vessel 49, the vessel 49 housing a tube 51 used to recirculate waterflowing through the jacket 53 of the second heat exchanger 25. Anelectrically powered fluid transfer pump (not shown) is used torecirculate water through the second heat exchanger 25. In this example,the third phase change substance comprises a third hydrate salt sodiumacetate trihydrate having a melting point of approximately 58° C. Thesecond accumulator 16 can take a variety of configurations and maycontain any selected phase change substance largely depending on theboiling-point of the refrigerant used.

The solar collector 18 can also take a variety of forms andconfigurations. Essentially the solar collector 18 comprises an uppersurface (not shown) exposed to sunlight, the upper surface constructedof a material having a relatively low reflectivity and radiation. Inthis embodiment the upper surface is coated with a coating ofIMPERSPRAY. IMPERSPRAY is a trade mark for a composite bitumen/latexproduct. The collector 18 has a base layer constructed of a high densitypolystyrene material having relatively high thermal insulation. Thecoating of IMPERSPRAY covers an upper surface of the base layer. Acorrugated sheet constructed of a polycarbonate material, beingsubstantially transparent to sunlight, rests on the coating ofIMPERSPRAY. A series of adjacent channels are thus defined between alower surface of the corrugated sheet and the coasting of IMPERSPRAY. Itis believed that a greenhouse heating effect occurs in the adjacentchannels such that the efficiency of the collector 18 is increased.

Water, in this example being the heat transfer fluid, is used totransfer waste heat, absorbed on the collector 18, to the secondaccumulator 16. The water is carried through the recirculation tube 42laid in a serpentine arrangement within the base layer underneath thecoating of IMPERSPRAY. In this example, heat from the solar collector 18is transferred to the third hydrate salt contained in the secondaccumulator 16 via the water flowing through the recirculation tube 42.The first hydrate salt contained in the second heat exchanger 25 is thenheated via the water recirculating between the second accumulator 16 andthe jacket 53 of the second heat exchanger 25.

Each of the first solenoid actuated valves 30A, 30B is designed toalternately supply refrigerant to each of the hydraulic cylinders 20.The refrigerant is released into the compressible chamber 40A, 40B ofeach cylinder 20A, 20B.

The condenser 32 can also take a variety of forms. In this example, thecondenser 32 comprises a refrigerant tube (not shown) formed in theshape of a helix in the condenser 32, the tube housed in a shell 55. Theshell 55 contains a second phase change substance, in this embodiment asecond hydrate salt, having a relatively high latent heat of fusion anda relatively low melting-point. The shell is jacketed with a suitableheat-insulation material. In this example the second hydrate saltcomprises a stoichiometric mixture of sodium chloride, calcium chlorideand demineralised water, having a melting point of approximately -21° C.

The pump 28 of this embodiment is a positive displacement pumpcomprising a series of gears used for generating a flow of refrigerantto the second heat exchanger 25. The pump 28 in operation is driven bythe hydraulic motor 22 via the endless belt 34.

As further shown in FIG. 1, each of the components of the oil 12 andrefrigerant 14 paths are connected so that a continuous flow path isprovided for the hydraulic oil and the refrigerant, respectively.Suitable tubing, couplings, and other attachments are used to connectthe components.

Located downstream of the incompressible fluid chamber 42A, 42B of eachhydraulic cylinder 20A, 20B there is a downstream non-return valve 48included in the hydraulic oil path 12. Located upstream of each of theincompressible fluid chambers 42A, 42B there is an upstream non-returnvalve 50 included in the hydraulic oil path 12. Downstream of thecompressible fluid chamber 40A, 40B of each hydraulic cylinder 20A, 20Bthere is a second pair of solenoid actuated valves 52A, 52B included inthe refrigerant path 14.

Operation of the thermo-volumetric motor 10 described above will now beexplained in some detail, by way of example only. Sunlight being a heatsource can be absorbed on the upper surface of the solar collector 18.Heat is then transferred from the solar collector 18 to the secondaccumulator 16 via water, being the heat transfer fluid in this example.The third hydrate salt, having a melting-point of approximately 58° C.contained in the vessel 49 of the second accumulator 16 is heatedwherein at least a portion of said salt fuses and stores energy in theform of latent heat. Thereafter water recirculating between the secondaccumulator 16 and the jacket of the second heat exchanger 25 cools andsolidifies a fraction of the third hydrate salt and is thus heated bythe latent heat of fusion of the third hydrate salt. The heated waterthen exchanges heat with the first hydrate salt contained in the secondheat exchanger 25 thereby fusing at least a portion of this hydratesalt.

The refrigerant flowing through the first tube of the second heatexchanger 25 causes the first hydrate salt to solidify thus releasingits latent heat of fusion. The hydraulic oil flowing through the shellof the first heat exchanger 24 can also exchange heat, in the form ofspecific heat, with the refrigerant thus preheating the refrigerantbefore it flows to the second heat exchanger 25. Advantageously thisreduces the heat required to be absorbed by the refrigerant from thefirst hydrate salt in order to effect vaporisation of the refrigerant.

The refrigerant when heated by the first hydrate salt expands,preferably vaporising, and flows to the first solenoid actuated valves30A, 30B. One of the first valves 30A then opens and releasespressurised refrigerant into the compressible fluid chamber 40A of oneof the hydraulic cylinders 20A. The second solenoid actuated valve 52Ais closed when the first valve 30A is opened. The other of the firstsolenoid actuated valves 30B is also closed.

The refrigerant then moves the piston 36A in a downward direction (asshown in FIG. 1) thereby driving the hydraulic oil contained in theincompressible fluid chamber 42A out of the cylinder 20A. The hydraulicoil then drives the hydraulic motor 22 which is coupled to and rotatesthe positive displacement pump 28 of the refrigerant path 14. The oilwhen forced out of the hydraulic cylinder 20A and through the downstreamnon-return valve 48 is heated and passes through the shell of the firstheat exchanger 24. The oil can then transfer heat, in the form ofspecific heat, to the refrigerant flowing through the tube of the heatexchanger 24. The volume ratio of oil contained in the incompressiblefluid chamber 42 when the piston 36 is moved from a top dead centreposition to a bottom dead centre position is approximately 7 to 1.

The second solenoid actuated valve 52A is opened once the piston 36A hasmoved a full stroke in the cylinder 38A and the oil forced from theincompressible fluid chamber 42A. Oil flows to the incompressible fluidchamber 42B of the other hydraulic cylinder 20B via the upstreamnon-return valve 50B. The piston 36B is then forced by the hydraulic oilin an upward direction (as shown in FIG. 1). When the piston 36B is atthe top of its stroke, the first solenoid valve 30B is opened with thesecond solenoid valve 52B closed wherein refrigerant is released intothe compressible fluid chamber 40B thus forcing oil from theincompressible fluid chamber 42B through the downstream non-return valve48B. The flow of oil through the oil path 12, as a result of thealternate reciprocation of each piston 36, drives the hydraulic motor 22which can the be used to provide motive power.

The opening and closing of the first and second valves 30, 52respectively can be controlled so that reciprocation of the pistons 36can be varied and thus timing of the motor 10 controlled. The motivepower can then, for example, be used to drive a generator therebyproducing electricity.

The positive displacement pump 28 when driven by the hydraulic motor 22pumps refrigerant to the first and second heat exchangers 24, 25 and thefirst solenoid actuated valves 30. The refrigerant when exhausted fromthe compressible fluid chamber 40 of each of the hydraulic cylinders 20flows to the condenser 32. In this example, the second hydrate saltcomprises a stoichiometric mixture of sodium chloride, calcium chloride,and demineralised water, having a melting-point of approximately -21° C.This is preferably less than the average temperature of the refrigerantwhen exhausted from each hydraulic cylinder 20A, 20B. The second hydratesalt thereby absorbs heat from the refrigerant in the form of latentheat as it passes through the condenser 32. The refrigerant therebycools and preferably condenses before being pumped downstream by thepositive displacement pump 28.

It will now be apparent to persons skilled in the relevant arts that thepresent invention has at least the following advantages over theadmitted prior art:

1) Solar energy or waste heat can be used to efficiently drive athermo-volumetric motor using a phase change substance having arelatively high latent heat of fusion;

2) A thermo-volumetric motor according to the present invention isrelatively efficient when compared to, for example, a solar poweredelectric motor;

3) The thermo-volumetric motor has no deleterious exhaust products andis relatively environmentally safe; and

4) The thermo-volumetric motor uses energy such as solar energy which isgenerally not a limited resource as, for example, is the case withmineral fuels.

It will be apparent to persons skilled in the relevant arts thatnumerous variations and modifications can be made to the apparatus andmethod relating to a thermo-volumetric motor in addition to thosealready mentioned above without departing from the spirit and basicinventive concepts of the present invention. For example, the heattransfer means may be heated by some other heat source other than solarenergy as described herein. For example, waste heat from a processstream may intermittently supply heat to the first phase changesubstance to effect storage of latent heat. The heat transfer meansand/or the cooling means may contain a different phase change substanceto that described and may in fact comprise banks of various phase changesubstances, each with a different melting-point. The heat transfer meansis not limited to the shell and tube type heat exchanger describedherein. Furthermore, the pump, hydraulic motor and injector describedmay take various forms, each form essentially performing the samefunction, and thus remain within the scope of the present invention. Thecondenser may not be activated by a second phase change substance butmay include some other cooling medium. The hydraulic oil orincompressible fluid may not exchange heat with the refrigerant orcompressible fluid as described herein. The thermo-volumetric motor doesnot require a second accumulator as herein described but may rely solelyon the first phase change substance contained in the heat transfer meansfor the storage of latent heat. Preferably the compressible fluid is nota halogenated hydrocarbon as herein described. All such variations andmodifications are to be considered within the scope of the presentinvention the nature of which is to be determined from the foregoingdescription.

We claim:
 1. A thermo-volumetric motor comprising:a continuousincompressible fluid path, adapted to carry a substantiallyincompressible fluid, said incompressible fluid path having pressuretransfer means and actuating means in fluid communication with eachother; a continuous compressible fluid path being adapted to carry asubstantially compressible fluid, said compressible fluid path includingheat transfer means in fluid communication with the pressure transfermeans, the heat transfer means including a first phase change substancehaving a relatively high latent heat of fusion, and cooling means influid communication with the heat transfer means and the pressuretransfer means whereby, in use, heat from a heat source can be absorbedby the first phase change substance so that at least a portion of thefirst phase change fuses and thereafter when said portion of the firstphase change substance solidifies and releases latent heat thecompressible fluid can absorb said latent heat and expand, thus movingthe pressure transfer means wherein the incompressible fluid is forcedalong the incompressible fluid path thus moving the actuating meanswhich can be adapted to provide motive power, the cooling meansthereafter cooling the compressible fluid after said compressible fluidis released from the pressure transfer means.
 2. A thermo-volumetricmotor as defined in claim 1 wherein the compressible continuous fluidpath further comprises a pump operatively coupled to the actuating meansand in fluid communication with the heat transfer means, the coolingmeans, and the pressure transfer means wherein movement of the actuatingmeans drives the pump thereby pumping the compressible fluid through thecompressible fluid path.
 3. A thermo-volumetric motor as defined inclaim 1 wherein the thermo-volumetric motor further comprises acollector in heat conductive communication with the heat transfer meanswhereby, in use, heat absorbed by the collector from a heat source canbe transferred to the first phase change substance included in the heattransfer means.
 4. A thermo-volumetric motor as defined in claim 1wherein the pressure transfer means comprises a piston slidably receivedin a cylinder defining a compressible fluid chamber on one side of thepiston, said compressible fluid chamber adapted to receive thecompressible fluid, and an incompressible fluid chamber on an oppositeside of the piston, said incompressible fluid chamber adapted to receiveincompressible fluid whereby, in use, expansion of the compressiblefluid as effected by the heat transfer means can move the pistonrelative to the cylinder thereby forcing the incompressible fluidthrough the incompressible fluid path.
 5. A thermo-volumetric motor asdefined in claim 1 wherein the pressure transfer means comprises a firstand a second piston each slidably received in a first and a secondcylinder, respectively, defining a compressible fluid chamber on oneside of the piston, said compressible fluid chamber adapted to receivethe compressible fluid, and an incompressible fluid chamber on anopposite side of the piston, said incompressible fluid chamber adaptedto receive the incompressible fluid whereby, in use, compressible fluidcan be expanded into the compressible fluid chamber of the firstcylinder wherein the first piston is moved relative to the firstcylinder thereby forcing the incompressible fluid through theincompressible fluid path and moving the second piston relative to thesecond cylinder, and thereafter compressible fluid can be expanded intothe compressible fluid chamber of the second cylinder.
 6. Athermo-volumetric motor as defined in claim 1 wherein the cooling meansis a first accumulator containing a second phase change substance havinga relatively high latent heat of fusion and a relatively lowmelting-point whereby, in use, heat from the compressible fluid can beabsorbed by the second phase change substance thus cooling thecompressible fluid passing through the cooling means.
 7. Athermo-volumetric motor as defined in claim 1 further comprising a heatexchanger in fluid communication with both the actuating means and thecooling means whereby, in use, heat generated by the incompressiblefluid when forced from the pressure transfer means can be transferred tothe compressible fluid via the heat exchanger thus expanding thecompressible fluid.
 8. A thermo-volumetric motor as defined in claim 7wherein the heat transfer means further includes the heat exchanger sothat heat generated by the incompressible fluid when forced from thepressure transfer means can be transferred to the compressible fluid viathe first phase change substance included in the heat transfer means. 9.A thermo-volumetric motor as defined in claim 3 wherein the collector isa solar collector adapted to absorb sunlight being the heat source. 10.A thermo-volumetric motor as defined in claim 1 wherein the actuatingmeans is a hydraulic motor.
 11. A thermo-volumetric motor as defined inclaim 1 wherein the heat transfer means comprises:a first tube adaptedfor carrying the compressible fluid through the heat transfer means; anda shell containing the first phase change substance said substance in,heat conductive communication with the first tube whereby, in use,latent heat can be transferred from the first phase change substance tothe compressible fluid via the first tube of the heat transfer means.12. A thermo-volumetric motor as defined in claim 11 wherein the heattransfer means further comprises a jacket surrounding the shell andadapted to carry a heat transfer fluid whereby, in use, heat from theheat transfer fluid can be transferred to the first phase changesubstance thereby melting the first phase change substance and storinglatent heat.
 13. A thermo-volumetric motor as defined in claim 12wherein the motor further comprises a collector in heat conductivecommunication with the heat transfer means and wherein the jacket is inheat conductive communication with the collector wherein heat absorbedby the collector can be transferred to the first phase change substancevia the heat transfer fluid.
 14. A thermo-volumetric motor as defined inclaim 13 wherein the heat transfer means further comprises a secondaccumulator containing a third phase change substance, said secondaccumulator in heat conductive communication with the collector, whereinthe heat transfer fluid can be preheated by the latent heat of the thirdphase change substance before said heat transfer fluid flows to thejacket.
 15. A method for producing motive power comprising the stepsof:absorbing heat, from a heat source, on a first phase change substanceincluded in heat transfer means wherein at least a portion of the firstphase change substance fuses, said first phase change substance having arelatively high latent heat of fusion; transferring latent heat from thefirst phase change substance, upon solidification thereof, to acompressible fluid thereby expanding the compressible fluid; releasingthe expanded compressible fluid into pressure transfer means thus movingthe pressure transfer means which then forces an incompressible fluidthrough an actuating means thus producing motive power from theactuating means; and cooling the compressible fluid and returning saidcompressible fluid to the heat transfer means.
 16. A method forproducing motive power as defined in claim 15 further comprising thestep of driving a pump operatively coupled to the actuating meanswherein the compressible fluid is pumped to the heat transfer meansusing the pump.
 17. A method for producing motive power as defined inclaim 15 further comprising the step of absorbing heat from the heatsource onto a collector, wherein the absorbed heat can be transferred tothe first phase change substance of the heat transfer means.
 18. Amethod for producing motive power as defined in claim 15 wherein thestep of cooling the compressible fluid involves absorbing heat from thecompressible fluid by exchanging heat with a second phase changesubstance, having a relatively high latent heat of fusion and arelatively low melting-point, wherein the compressible fluid is cooled.19. A method for producing motive power as defined in claim 15 furthercomprising the step of transferring specific heat from theincompressible fluid, said specific heat generated when theincompressible fluid is forced from the pressure transfer means, to thecompressible fluid via a heat exchanger.
 20. A thermo-volumetric motoras defined in claim 1 wherein the first, second and/or third phasechange substances are first, second and/or third hydrate salts,respectively, each having a relatively high latent heat of fusion.
 21. Athermo-volumetric motor as defined in claim 20 wherein the first hydratesalt and the third hydrate salt has a melting-point of between 0° C. to100° C.
 22. A thermo-volumetric motor or a method for producing motivepower as defined in claim 20 wherein the first hydrate salt and thethird hydrate salt each has a latent heat of fusion of greater than 50kilocalories/liter (kcal/l).
 23. A thermo-volumetric motor as defined inclaim 20 wherein the first hydrate salt and/or the third hydrate saltcomprises sodium acetate trihydrate or a derivative thereof.
 24. Athermo-volumetric motor as defined in claim 20 wherein the secondhydrate salt has a melting-point of less than 0° C.
 25. Athermo-volumetric motor as defined in claim 20 wherein the secondhydrate salt comprises a stoichiometric mixture of sodium chloride,calcium chloride, and demineralised water.
 26. A thermo-volumetric motoras defined in claim 1 wherein the incompressible fluid is a liquidhydrocarbon, such as oil or a derivative thereof.
 27. Athermo-volumetric motor as defined in claim 1 wherein the compressiblefluid is a refrigerant such as methane, chloro-difluoro or a derivativethereof.
 28. A thermo-volumetric motor as defined in claim 27 whereinthe refrigerant does not contain a halogen element.